But activists didn't let that stop them from making their message heard.

"The shoes are marching for us," one Parisian man, René Stroh, told me.

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I came upon the display, which had the feel of a public art instillation in front of the Place de la République, not far from the site of the recent shootings. It was the perfect, somber response to the ban on mass protests ahead of the COP21 U.N. climate change talks. Handwritten messages on the shoes called for the world to abandon fossil fuels and avoid the most disastrous impacts of climate change.

"The shoes are marching for us," said René Stroh of Paris.

The shoes asked dignitaries -- 140 of whom, including U.S. President Barack Obama, will be here for the summit -- to consider their children and generations that will inherit this planet from us. A troupe of Australian women dressed as "climate angels" walked speechlessly through the rows of shoes, underscoring the gravity of both the recent terror attacks here and the persistent threat of climate change.

"It's important not to stay too sad," said Murielle Ellert, a 38-year-old accountant whose shoes were among those on display. "We have to continue to live exactly like we did" before the attacks.

Climate activists organized a silent march in Paris on Sunday to avoid defying a ban on mass protest on Sunday, November 29. More than 140 world leaders are gathering in Paris for high-stakes climate talks that start Monday, and activists are holding marches and protests around the world to urge them to reach a strong agreement to slow global warming.

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Police fight with activists during a protest ahead of the 2015 Paris Climate Conference at the Place de la République.

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A man is detained November 29 by police at the Place de la République, where the candles and flowers were set in memory of the victims of the Paris terror attacks earlier in the month.

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Hundreds of pairs of shoes are displayed at the Place de la République.

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Women dressed as angels pose at the Place de la République.

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Climate change demonstrators march to demand curbs to carbon pollution in London.

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Protesters march down Piccadilly during the London demonstration.

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Climate activists march in front of the Brandenburger Tor in Berlin.

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Activists of the World Wildlife Fund wearing endangered species costumes perform at the Revolution Monument in Mexico City.

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People take part in the Global Climate March in Bogota, Colombia.

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A woman holds a sign reading "No more plastic bags" during a march in Santiago, Chile.

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Climate march participants gather in front of the Helsinki Cathedral in Helsinki, Finland.

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People hold flags and placards while marching in Amsterdam.

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Protesters wearing penguin costumes march in Vienna, Austria.

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People dressed in white crowd form a human glacier in Munich, Germany.

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People form a human chain in Nantes, France.

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Some 700 people from different climate justice movements gather in the Johannesburg, South Africa, focusing on the continued reliance of coal as a primary source of generating electricity.

We shouldn't ignore threats from ISIS and other extremists, and we must take time to honor the victims of the terror attacks in Paris and Lebanon, and to respect the lives that will be forever changed by their absence. But climate change is deserving of our attention as well.

The display of shoes at the Place de la République, which was organized by a group called Avaaz, gave way around noon to a "human chain" of activists that stretched down Boulevard Voltaire and up to the Bataclan, the music venue where so many were shot and killed.

"We were in a state of emergency before the attack, and we will still be in a climate state of emergency after the attack" because of climate change, said Eros Sana of 350.org, a climate activist group that helped organize the human chain. "We decided to do something that is not a banned demonstration."

Along the chain, I met a woman dressed as a clown and wearing goggles and a snorkel ("We know the water is going up and we are ready," she said in a French accent), as well as Helene Hohmeier, a 53-year-old woman wearing a polar bear hat ("The ice is melting. It's very urgent to do a lot of something"). Corentin Leblanc, a 20-year-old wearing a stocking cap and a massive backpack, pulled me aside to say he'd walked 600 kilometers (373 miles) from The Netherlands to Paris for the demonstration.

The show of solidarity was respectful and moving. It effectively conveyed a reverence for the tragedy that still cloaks this city and the urgency with which we need to act on climate change.

I was saddened, however, to see protests become heated later in the day.

After the silent-shoe demonstration and the human chain had dispersed, by about 1 p.m., a group of activists that 350.org claims are "unaffiliated with the climate movement" amassed on the Place de la République. They challenged the ban on marching and were met with police in riot gear who fired tear gas into the crowd. One demonstrator, a bandana pulled over his face, grabbed a CNN cameraman and tried to remove him and his camera from the scene.

They chanted for liberty and for the closing of all factories -- an end to market consumerism. It all had a militant, combative tone.

I understand the emotional charge behind the COP21 climate talks. The world has waited far too long to move toward a cleaner-energy future. I'm frustrated, too. But I found the morning's silent demonstrations to be far more effective and respectful.

I hope the U.N. climate talks, which continue at least through December 11, will foster productive dialogue and real, substantial change. Not conflict and animosity. There's no time for that, not anymore. It's now time -- during what likely will be the hottest year on record -- for us to realize that we need to work together to implement solutions to this crisis.